According to Special Relativity the velocity of light is limiting: no matter how objects alter their velocity relative to one another, the sum of their velocities can never exceed the ultimate constant c (the velocity of light in a vacuum); moreover, the measurement of c is unaffected by the velocity of the measurer. The apparently paradoxical implications of this statement are avoided because objects travelling at high velocities relative to one another are subject to different frames of measurement, by which each appears to the other to be subject to a distortion of time. As a consequence, Spaceships which make interstellar journeys at velocities close to light-speed relative to their points of origin are subject to a time-dilation whereby the travellers age more slowly than the people they left at home. A good popularization of such ideas can be found in George Gamow's book of scientific fables Mr Tompkins in Wonderland (coll 1939 chap).

Some "relativistic" effects of FTL travel are described in Camille Flammarion's pre-Einsteinian cosmic fantasy Lumen (1887; trans anon 1892) [for further publication details see Flammarion], but other early sf writers, including the pioneers of pulp Space-Opera, ignored such matters, even after Relativity theory had come into being and Special Relativity in particular had been extensively tested by experiment. E E Smith's early Skylark and later Lensman stories show a typically joyous disregard for any such natural speed limits. As the intellectual respectability of such ignorance declined, however, the limiting velocity of light increasingly became an awkward inconvenience to writers of interstellar adventure stories, necessitating the development of a series of facilitating devices – often involving "space-warps", interdimensional dodges into Hyperspace or "subspace", or, more recently, Tachyon drives or Black-Hole-related Wormholes – to enable the science-fictional imagination to retain Galactic Empires and their effectively infinite supply of earthlike Alien worlds ripe for Colonization. Instantaneous Matter Transmission is another very popular FTL device.

Perhaps less obviously, faster-than-light Communication systems such as Ultrawaves, James Blish's Dirac Communicator and Ursula K Le Guin's Ansible (which see for discussion of further sf names for FTL communicators) require closely similar justificatory fudging. Indeed Orson Scott Card's Xenocide (1991) and the "churten physics" stories included in Le Guin's A Fisherman of the Inland Sea (coll 1994) both acknowledge that FTL communication via Ansible implies the possibility of FTL Space Flight. Earlier, Robert A Heinlein's Time for the Stars (1956) first deployed – literally – the celebrated "twins paradox" of Relativity and then used its twins' posited ability to stay in contact by instantaneous Telepathy as a refutation of the relativistic paradigm, opening the way for FTL spaceships operating by the new Physics of "irrelevance".

None of these literary devices can in fact bypass the deeper logical difficulties which arise from Einstein's theory, but FTL drives of various kinds are so very useful in avoiding the inconveniences of Generation Starships that many writers of Hard SF insist on clinging to the hope that the theory may be imperfect in such a way as to permit an exploitable loophole. Faster than Light (anth 1976), a theme anthology edited by Jack Dann and George Zebrowski, includes, as well as the stories, several essays combatively arguing the case. Other writers, however, have found the time-dilation effects associated with relativistic star-travel a rich source of plot ideas (see Relativity).

John W Campbell Jr was the writer who laid the groundwork for such facilitating devices as the space-warp in Islands of Space (Spring 1931 Amazing Stories Quarterly; 1957) and hyperspace in The Mightiest Machine (December 1934-April 1935 Astounding; 1947), where the term made its debut; where he led, legions followed. Stories which work harder than most to make such notions plausible include Robert A Heinlein's Starman Jones (1953), Murray Leinster's The Other Side of Nowhere (1964), A Bertram Chandler's Catch the Star Winds (1969) and David Zindell's Neverness (1988). Memorable imagery relating to hypothetical means of FTL travel can be found in James Blish's tales of cities-become-starships by courtesy of the Spindizzy, Cities in Flight (omni 1970), and in Kenneth Bulmer's "Strange Highway" (April 1960 Science Fantasy) and Bob Shaw's The Palace of Eternity (1969). Many sf stories suggest that the pilots of FTL spaceships may have to be specially adapted to the task, sometimes by cyborgization (see Cyborgs), becoming more-or-less alienated from their own kind; notable examples include Cordwainer Smith's "Scanners Live in Vain" (January 1950 Fantasy Book #6), Anne McCaffrey's The Ship Who Sang (coll of linked stories 1969), Gerard F Conway's Mindship (1974), Kevin O'Donnell Jr's Mayflies (1979), Joan Cox's Star Web (1980), Vonda N McIntyre's Superluminal (1984), Melissa Scott's trilogy begun with Five Twelfths of Heaven (1985), and Emma Bull's Falcon (1989).

Norman Spinrad's The Void-Captain's Tale (1983) deals ironically with sf symbolism of this general kind, featuring a phallic spaceship powered by a libidinous "psychological drive". Many other space drives of generally unspecified operation are casually proposed in sf: examples include the "Haertel overdrive" of James Blish's "Common Time" (August 1953 Science Fiction Quarterly) and the "Blieder-drive" of Eric Frank Russell's The Great Explosion (fixup 1962). Some are intentionally absurd, like the "Bloater Drive" which in Harry Harrison's Bill, the Galactic Hero (December 1964 Galaxy as "The Starsloggers"; exp August-October 1965 New Worlds; 1965) weakens interatomic forces until the hugely expanded, insubstantial ship spans the entire interstellar distance to be traversed: the process is then reversed with the ship (somehow) anchored at its destination. M John Harrison satirized all such wild and wonderful drives in his review column title "To the Stars and Beyond on the Fabulous Anti-Syntax Drive" (in New Worlds Quarterly 5, anth 1973, ed Michael Moorcock).

A relevantly themed anthology is Faster than Light (anth 1976), edited by Jack Dann and George Zebrowski. The endless possibilities of Imaginary Science FTL facilitating devices will undoubtedly continue to do sterling work for the extravagantly inclined sf writer. [BS/DRL]

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